What would happen is we would always get the Heavensward alliance raids and then eventually get sick of those as well. Or, whichever one the majority of people in queue tend to have unlocked.

I believe far less people queue for Main Scenario roulette. Because of that, new players would struggle to fill the queue as often and struggle to progress MSQ as fast. As such, mentor roulette may begin to match you into CT, which in my experience it has never, ever done except "in progress" when someone exits and needs a refill.